It is well-known that lead-containing brass alloys such as CuZn40Pb1, C36000, C3604 and C3771 usually contain 1.0-3.7 wt % Pb for ensuring excellent free-cuttability.
Lead-containing brass alloys are still widely used in the manufacture of many products due to their excellent cuttability and low cost. However, Pb-contaminated steam produced by the process of smelting and casting lead-contained brass alloy and Pb-contaminated dust produced in the process of cutting and grinding the lead-contained brass alloy are harmful to the human body and the environment. If the lead-containing brass alloys are used in drinking-water installations such as faucets, valves and bushings, contamination of the drinking water by Pb is unavoidable. In addition, toys which are produced by Pb-containing brass alloys are more harmful, as they are touched frequently, thus increasing potential exposure to Pb.
Ingestion of lead by humans is harmful, so the use of lead is being strictly banned by law in many countries due to the concerns on health and environment. For dealing with this challenge, metallurgists and manufacturers of copper materials actively research and develop lead-free free-cutting brass alloys.
For example, Hofmann et al. in US20040241038 disclose a lead-free copper alloy composition. However, US20040241038 teaches away from adding more than 0.2 wt % P, stating that “above 0.2% [of P], however, the disadvantages would be predominant.” US20040141038 para. [0037]. US20040241038 also does not disclose an alloy containing less than 0.5 wt % Sn. The alloy disclosed in US20040241038 also requires the expensive element Ni.
In the different and unrelated context of providing an alloy for electric connectors, JP 2002038246 discloses a so-called Colson alloy that may be lead free. JP2002038246 does not teach an alloy containing relatively high levels of P and Mg. A so-called Colson alloy is a Cu—Ni—Si based alloy. Therefore, the alloy of JP2002038246 requires the expensive element Ni. JP2002038246 does not teach a tin-free alloy. JP2002038246 does not address the alloy's cuttability or machinability.
Some lead-free free-cutting brass alloys use Si instead of Pb, but the cuttability is not remarkably improved and the cost increases due to the high quantity of copper. Therefore, silicon brass alloys are not commercially competitive at present. One commonly used type of lead-free free-cutting brass alloy is a bismuth brass alloy, which uses bismuth instead of Pb. Many kinds of bismuth brass alloys with high or low zinc have been developed and their formal alloy grades have been registered in the United States. These kinds of brass alloy contain valuable tin, nickel and selenium as well as bismuth. For example, Kurose et al. in US 20070243096 discloses such an alloy. Although their cuttability is 85%-97% of lead-contained brass alloy C36000, their cost is far higher than lead-contained brass alloy C36000. Therefore, these kinds of bismuth brass alloys are not competitively priced. Bismuth brass alloys also have been researched and developed in Japan and China and filed in their Patent Office. Considering that bismuth element is expensive, rare in the reserves and has poor cold and hot workability, using a bismuth brass alloy instead of a lead-containing brass alloy may be financially problematic. The invention of a free-cutting antimony brass alloy which use Sb instead of Pb has been patented in China (ZL200410015836.5). A corresponding U.S. application (US2006/0289094) is currently pending. There is, therefore, a need for a lead-free, tin-free, bismuth-free free cutting brass alloy that has excellent integrated performance at a reduced cost.